1. Field of the Invention
This invention relates to a method and apparatus for conveying a flexible, imperforate member through a liquid and, more particularly, to a method and apparatus for conveying a photographic material through a liquid or a series of liquids in a photographic development process.
2. Description of the Prior Art
Photographic paper or photographic film is generally made up of a base onto which an emulsion is coated. The base is primarily composed of a plastic material. The emulsion coating on the base is substantially a gel which is light sensitive. Usually, the gel consists of several layers with each layer being sensitive to a certain wave length of light or a certain color of light.
Prior to the gel or emulsion being exposed to various liquid chemical baths in photographic processing, the gel or emulsion is relatively sturdy and is not very susceptible to damage through normal handling. When this emulsion, however, is subjected to a series of liquid chemical baths, such as in photographic processing, the emulsion becomes very soft. In its soft state, this emulsion can scratch easily. Therefore, extreme care must be taken in photographic processing to avoid scratching of or damage to the photographic film or photographic paper. For example, a slight scratch on a negative can cause a large scratch on an enlarged print that is made from that negative.
Additionally, care must be taken in the particular photographic process to insure that the photographic paper or photographic film does not become significantly overdeveloped or underdeveloped in the various chemical baths. Further, in most present photographic processing apparatus, careful monitoring during the development process must be maintained to avoid loss or damage to the photographic film or photographic paper from causes inherently related to a particular apparatus.
One of the commonly known devices used in photographic processing is the roller transport processor. In this processor, a plurality of rollers are positioned in each of the various tanks containing the various liquid chemical baths of a photographic process. The photographic paper or photographic film is fed between pairs of driven rollers and the rollers convey the photographic paper or photographic film through a liquid chemical bath. In most cases, a U-shaped configuration of roller pairs is used in each liquid chemical bath of a photographic process. Using such a U-shaped configuration, the photographic paper or photographic film is pulled down through a liquid chemical bath to the bottom of a tank and then back up through the liquid chemical bath, following the U-shaped path provided by the rollers in the bath.
With the roller transport apparatus, various problems are present. If there is any foreign matter on any one of the rollers, it is likely to cause a scratch on the photographic paper or photographic film. Further, if the photographic paper or photographic film, for any number of reasons, does not proceed smoothly through a pair of rollers or a series of pairs of rollers, scratching or other physical damage to the photographic paper or photographic film can occur.
Since the time the photographic paper or photographic film is in a chemical bath may be critical to proper processing, any delay or jamming of the photographic paper or photographic film in a roller transport processor may also produce an unacceptable overdeveloping of the photographic paper or photographic film. One of the more serious problems associated with the roller transport processor, however, is that the photographic paper or photographic film could become torn or creased by the rollers. If the original photographic film is being processed and such should occur, the damage to the film may be permanent and irreversible.
In the roller transport method, a turn guide is often times employed to carry the photographic paper or photographic film from one liquid chemical bath to another liquid chemical bath. The turn guide is generally a curved piece of plastic or metal which is positioned adjacent to and between liquid chemical baths.
Other apparatus commonly used in the development of photographic film or photographic paper is commonly referred to as hanger transport devices. The photographic paper or photographic film is usually pinned to a hanger which is connected to a device for submerging and removing the photographic paper or photographic film from the various liquid chemical baths in the process.
A common problem associated with the hanger transport apparatus is that, if the photographic paper or photographic film is not properly secured to the hanger when it is lowered into a liquid chemical bath, the motion of raising or lowering may jar the photographic paper or photographic film loose so that it falls off the hanger, thereby remaining in the liquid chemical bath. If such should occur, overdevelopment of the photographic paper or photographic film in the bath occurs especially if the loss of the film from the hanger is not readily noticed.
A second problem is universally present with the hanger transport apparatus. The photographic paper or photographic film is usually arranged in a vertical manner from the hanger, and the photographic paper or photographic film generally enters and leaves a liquid chemical bath in a vertical direction. With this arrangement, the photographic paper or photographic film on the bottom hanger enters the chemical bath first and commences development prior to the photographic paper or photographic film in the middle or top of the hanger. When the photographic paper or photographic film is removed from the chemical bath, the photographic paper or photographic film near the top of the hanger leaves the bath before the middle or the bottom of the arrangement. If not carefully controlled, overdevelopment or underdevelopment or both could occur.
Other apparatus often used in photographic processing is the leader transport apparatus. The photographic paper or photographic film is either taped, stapled, clipped or attached by some appropriate means to a leader. Usually, the leader is made of plastic. The leader is driven through the chemical bath or baths in the process, usually by means of a series of rollers similar to that previously discussed. Generally, only the leader is driven and the photographic paper or photographic film, which is attached to the leader, is pulled through the chemical bath. The leader can be either an endless leader, which is in the form of a continuous belt, or could be a single piece of material which is fed through the various baths. If care is not taken to attach the photographic paper or photographic film properly to the leader, it may detach in the process. If it should detach, the photographic paper or photographic film may become damaged through possible scratching or tearing. Also, if the film should become disengaged from the leader, it may fall to the bottom of the chemical bath and may be subjected to damage from overexposure from the chemical action in the bath. It is also possible that the leader may break, causing problems similar to those mentioned above.
Examples of other photographic apparatus and methods are disclosed in the following United States patents. U.S. Pat. No. 3,690,758 to Knechtel et al. discloses a developing apparatus for electrophotographic use. The apparatus includes a tank containing developing liquid, a cylinder having an apertured side wall supported for rotation in the tank, and a propeller within the cylinder for creating reduced pressure therein. Sheets of paper having an electrostatic latent image formed thereon are attracted to the cylinder and maintained in contact therewith by suction. After development, the sheets of paper are peeled from the cylinder by elongated comb tooth members.
U.S. Pat. No. 4,003,070 to Merz et al. discloses apparatus for treating photographic materials. In Merz, a pair of drums is mounted for rotation about parallel axes. Channel forming walls are provided adjacent the drums. Such channel forming walls define a first channel section and a second channel section surrounding the circumference of the drums with the channel sections merging with one another in a gap between the drums. Circulating means is provided to circulate a treating fluid through the channel sections. The photographic material is fed sequentially through the first and second channel sections. Suction is employed to draw the photographic material against the rotating drums.
U.S. Pat. No. 4,208,121 to Muller discloses apparatus for developing latent images of X-ray objects on dielectric receptor sheets. In Muller, two identical sheet carriers constituting a segment of a cylinder and extending along an arc of less than 180.degree. rotate about a horizontal shaft. Suction ports are provided in the peripheral surfaces of the carriers to attract the receptor sheets during rotation of the carrier.
There is need for a relatively simple, effective, and efficient method and apparatus for transporting photographic material, such as photographic film or photographic paper, through a liquid or various liquids in the photographic processing of the photographic material. Such method or apparatus should also significantly minimize damage to the photographic material from scratching, tearing or from adverse chemical action on the photographic material, such as from overexposure or underexposure.